1. Field of Invention
The present invention relates generally to semiconductor processing equipment. More particularly, the present invention relates to a modular stage device that provides reaction force cancellation, allows the center of gravity of components of the stage device to remain substantially unchanged during operation, and is both readily accessible and serviceable.
2. Description of the Related Art
For precision instruments such as photolithography machines which are used in semiconductor processing, factors which affect the performance, e.g., accuracy, of the precision instrument generally must be dealt with and, insofar as possible, eliminated. When the performance of a precision instrument is adversely affected, as for example by pitching moments, products formed using the precision instrument may be improperly formed and, hence, function improperly. For instance, a photolithography machine that is subjected to pitching moments may cause an image projected by the photolithography machine to move, and, as a result, be aligned incorrectly on a projection surface such as a semiconductor wafer surface.
Scanning stages such as wafer scanning stages and reticle scanning stages are often used in semiconductor fabrication processes, and may be included in various photolithography and exposure apparatuses. Wafer scanning stages are generally used to position a semiconductor wafer such that portions of the wafer may be exposed as appropriate for masking or etching. Reticle scanning stages are generally used to accurately position a reticle or reticles for exposure over the semiconductor wafer. Patterns are generally resident on a reticle, which effectively serves as a mask or a negative for a wafer. When a reticle is positioned over a wafer as desired, a beam of light or a relatively broad beam of electrons may be collimated through a reduction lens, and provided to the reticle on which a thin metal pattern is placed. Portions of a light beam, for example, may be absorbed by the reticle while other portions pass through the reticle and are focused onto the wafer.
FIG. 1 is a diagrammatic representation of a conventional stage apparatus, e.g., a wafer scanning stage apparatus. A stage apparatus 100 includes a coarse stage 104 which is arranged to scan in a y-direction 128. Coarse stage 104, which may carry a wafer table (not shown) positioned atop a fine stage (not shown), is coupled to coils 108 which are arranged to cooperate with magnet tracks 112 to drive coarse stage 104. Specifically, coil 108a and magnet track 112a are positioned on one side of coarse stage 104 while coil 108b and magnet track 112b are positioned on an opposite side of coarse stage 104.
Reaction forces generated by motors which include coils 108 and magnet tracks 112 are effectively guided to a grounding surface 116.
Typically, reaction forces generated by motors (not shown) which allow coarse stage 104 to be scanned in an x-direction 120 are also absorbed by a grounding surface such as grounding surface 116. When differential movement of coil 108a and coil 108b, e.g., when coil 108a and coil 108b are not scanned at the same velocity, allows for rotational motion of coarse stage 104 about a z-direction 124, reaction forces generated from such movement may also be absorbed by a grounding surface such as grounding surface 116.
Although a stage apparatus such as stage apparatus 100 is generally effective in enabling a wafer (not shown) positioned atop coarse stage 104 to be positioned, such a stage apparatus may be both difficult to access and difficult to service. That is, since coils 108 are located on both sides of coarse stage 104, the design of stage apparatus 100 is such that a debugging process to isolate problems with stage apparatus 100 is relatively time consuming. By way of example, testing scanning capabilities in y-direction 128 is generally not possible unless stage apparatus 100 is substantially completely built. To correct problems observed when scanning capabilities in y-direction 128 are tested, substantially all of stage apparatus 100 may need to be dismantled. Hence, the accessibility and the serviceability, e.g., maintainability, of stage apparatus 100 may be somewhat lacking.
Therefore, what is needed is a method and an apparatus for enabling a stage apparatus which is relatively accessible and relatively serviceable, while being capable of operating such that disturbances within the stage apparatus are substantially minimized. In other words, what is desired is a stage apparatus which is relatively modular, and has a stage which may be driven through its center of gravity in order to minimize disturbances within the stage apparatus.